The present invention relates in general to flexible window wiping devices and, more particularly, to flexible windshield wiping devices.
A common defect in conventional automotive windshield wipers is observed when the surface which has been wiped on the windshield is left with bands or streaks. This defect is at least partially due to the failure of the wiper assembly to apply a uniform wiping force against the length of the wiper blade and thus also to the surface of the windshield. The lack of uniformity in the wiping force applied to the wiper blade is characterized by conventional wiper assemblies having superstructures which apply a force load upon the wiper blade at only relatively widely spaced intervals. As a result little, if any, force may be available at various locations between these spaced intervals.
Although the field of windshield wipers encompasses a relatively large number of issued patents depicting a variety of different designs, it may be fairly said that windshield wiper designs generally depict a commonality of approaches to their basic function. Thus, most windshield wipers are characterized by a superstructure which distributes the force applied by the central wiper arm, an intermediate wiper blade support member, and a flexible wiper blade insert which directly performs the function of wiping the windshield. Just as the great variety of windshield wiper designs share a certain commonality of structure, they also share certain disadvantages in carrying out the basic task at hand. For example, modern windshield wiper assembly designs must have some type of force distributing means to distribute the force applied by the wiper arm along the length of the flexible wiper blade. This is necessary because the wiper blade needs to be able to flex along its length in order to remain in wiping contact with a windshield surface having a varying radius of curvature. Conventional wiper assemblies typically employ a superstructure having a primary yoke attachable to the wiper arm and a pair of secondary yokes attached at each end of the primary yoke and which serve to distribute the force exerted on the superstructure from the wiper arm at four evenly spaced intervals along its length. Since these intervals are still rather widely spaced little, if any, force may be available at various locations between these intervals. Thus, while this design provides some measure of increased force distribution along the length of the wiper blade, it is inherently incapable of providing or even approaching to provide equal force distribution at all points along the length of the blade.
Various attempts have been made to improve the distribution of force applied by the wiper arm along the length of the wiper blade. For example, U.S. Pat. No. 3,104,412 to Hinder discloses a resilient backing member or superstructure made of molded plastic having a concave face with a curvature substantially equivalent to the maximum curvature of the wiped windshield surface. The backing member is directly attached to the flexible wiper blade. This arrangement is believed to be inherently unable to provide equal force distribution when the radius of curvature varies along the length of the blade.
U.S. Pat. No. 4,028,770 to Appel discloses a windshield wiper blade assembly having a single piece resilient backbone member or superstructure. Uniform wiping pressure is assertedly achieved by forming the superstructure so as to have a uniform radius of curvature which is less than that of the windshield surface to be traversed together with varying the width and/or thickness of the superstructure from a maximum through the central arm attachment point to a minimum through the central arm attachment point to a minimum at the opposite ends thereof, with the width and/or thickness and degree of curvature being proportioned or correlated with the modulus of elasticity, load and length of the blade. This design, as well as that in the aforementioned U.S. Pat. No. 3,104,412 suffer the inherent disadvantage that each superstructure's shape will need to be varied for each differently shaped windshield, thus making standardization difficult, if not impossible to obtain. A further disadvantage results from the fact that the pressure distribution design is incorporated in a single piece superstructure preventing its adaption to existing conventional type superstructures.
In my U.S. Pat. No. 4,342,129 issued Aug. 3, 1982, I disclosed the use of a pre-stressed convex shaped intermediate support member between a conventional type superstructure and wiping blade which serves to more uniformly distribute along the length of the wiper blade the forces applied by the superstructure at spaced intervals. A pre-stressed convex shaped flexor element having a similar function is disclosed in U.S. Pat. No. 2,290,336 to Anderson. While I have found the type of approach incorporated in this design to offer some improvement in force distribution between the force application spaced intervals in conventional superstructures, this design still results in undesirable force variations along the wiper blade length and it involves difficult and costly procedure to pre-stress the intermediate support member. The present invention solves such problems in that it offers improved force distribution characteristics while at the same time being easier to manufacture than the above-mentioned devices.
Another problem which is encountered in wiping windshields involves the design of the flexible wiping blade or insert. The majority of wiping insert designs incorporate a blade which tapers to a relatively narrow lip which is bent from side to side as it wipes the windshield surface by contact with the side surface of the lip. The problems of this type of design are outlined in my aforementioned U.S. Pat. No. 4,342,129 which is hereby incorporated in this application for all purposes. As I disclosed therein, the use of the rolling sector type wiping insert provides a more advantageous design which permits the wiping surface to configure an edge in order to scrape the windshield surface rather than merely slide across it. However, due to non-conformal differences which may occur between the surface of the windshield and the wiping element retainer it has been found that portions of the surface area immediately adjacent to the contacting edge may become compressed into contact with the windshield. The present invention solves such problems by providing a radial clearance behind the contacting edge and/or lagging the contacting edge so that the windshield surface is not tangent to the rolling sector at any point except the edge.
Non-conformal differences between the wiped surface and the wiping element retainer can occur either as a result of the inability of the wiper assembly to follow the surface contour of the wiped surface or from any variations in the spring load which holds the wiper blade against the wiped surface. The present invention also provides improvements to the rolling-sector type wiping insert disclosed in my U.S. Pat. No. 4,342,129 which provide for an adequate range of elastic deformation when under normal load. Thus, small variations plus or minus from normal load or non-conformal surface to retainer element deviations will not adversely effect wiping efficiency.